1. Field of the Invention
The present invention relates to industrial automation systems and, more particularly, to a method for redundant message transmission in an industrial communication network.
2. Description of the Related Art
Usually, an industrial automation system comprises a multiplicity of industrial automation devices that are networked to one another via an industrial communication network and are used in the course of production or process automation to control or regulate installations, machines and devices. On account of time-critical constraints in technical systems that are automated via industrial automation devices, industrial communication networks predominantly use realtime communication protocols, such as Profinet, Profibus or realtime Ethernet, for communication between automation devices.
Interruptions in communication links between computer units of an industrial automation system or industrial automation devices are extremely problematical, because this can result not only in loss of information but also, for example, in undesirable or unnecessary repetition of a transmission of a service request. This causes additional utilization of communication links of the industrial automation system, which can result in further system faults or errors. Furthermore, messages that are not or not completely transmitted can prevent an industrial automation system from changing to or remaining in a safe operating state, for example. In the worst case, failure of a complete production installation and costly production stoppages can occur. Particular problems in industrial automation systems regularly result from message traffic with a relatively large number of, but relatively short, messages, which intensifies the above problems.
In order to be able to compensate for failures in communication links or devices, communication protocols, such as Media Redundancy Protocol, High-availability Seamless Redundancy, Parallel Redundancy Protocol or (Rapid) Spanning Tree Protocol, have been developed for high-availability, redundantly operable industrial communication networks.
Media Redundancy Protocol (MRP) is defined in International Electro Technical Commission (IEC) standard 62439 and allows compensation for single connection failures in networks with a simple ring topology in the event of bursty redundant transmission of messages. In principle, bursty media redundancy methods can be implemented with relatively little complexity. However, a disadvantage is that firstly messages can be lost in the case of error and, secondly, there is initially a fault state during reconfiguration of a communication network. Such a fault state needs to be backed up by a superimposed communication protocol, for example by means of TCP/IP at network or transport layer level, in order to prevent an interruption in a communication link.
High-availability Seamless Redundancy (HSR) and Parallel Redundancy Protocol (PRP) are defined in IEC standard 62439-3 and allow smooth redundant transmission of messages, particularly without changeover bursts in the event of topology changes. Based on High-availability Seamless Redundancy and Parallel Redundancy Protocol, each message is duplicated by a sending communication device and is sent to a receiver in two different ways. A receiver-end communication device filters out redundant messages that are duplicates from a received data stream.
In a redundant HSR or PRP communication network, a network component that provides access to the redundant communication network can assume different roles. Such a network component that conveys telegrams between subscribers or terminals in an HSR or PRP communication network, on the one hand, and terminals or network segments without HSR/PRP functionality, on the other hand, is called an HSR/PRP proxy or RedBox. In principle, a network component can connect a plurality of HSR rings or convert communication between HSR and PRP network segments for the purpose of accessing a redundant HSR or PRP communication network. In this case, the network component is called an HSR-HSR coupler or QuadBox or HSR-PRP coupler.
EP 2 165 474 A2 discloses a method for operating a network that has a switch and also network infrastructure devices connected thereto. The switch is controlled by a control unit. A redundancy unit connected between the switch and the control unit analyzes a data stream between the switch and the control unit and inserts data into the data stream or removes data from the data stream on the based on an analysis result.
EP 2 282 452 A1 describes a method for data transmission within a ring-like communication network, in which the data transmission occurs based on High-availability Seamless Redundancy and the communication network comprises at least a master node, a source node and a destination node. Each node has a first and a second communication interface with a respective first and second neighboring node. Furthermore, each node receives data frames via the first communication interface and forwards the received data frame in either altered or unaltered form via the second communication interface without additional delay. The master node sends a first and a second redundant data frame or an empty data frame to its first or second neighboring node. When the two redundant data frames are received, the source node fills the respective data frame in a predetermined reserved area with process data. Next, each filled data frame is immediately and individually forwarded to the first or second neighboring node of the source node. Finally, the destination node extracts the process data from the first received filled data frame in a pair of redundant data frames.
EP 2 413 538 A1 discloses a method for redundant communication in a communication system that comprises a plurality of communication networks. The communication networks are connected to one another via at least one coupling node. Transmission of data that come from a first communication network back to the first communication network from a second communication network is prevented based on a piece of information that is defined prior to data transmission.
Methods for smooth redundant transmission of messages in accordance with High-availability Seamless Redundancy or Parallel Redundancy Protocol are limited in their application to network topologies having ring structures or having a plurality of redundant communication networks that are constructed separately from one another.